1. Field
An aspect of the invention is related to a wireless communication apparatus, a transmitting method, and a receiving method for retransmitting.
2. Description of the Related Art
At present, a W-CDMA system as a third generation (3G) wireless communication system has been in widespread use. Moreover, a specification called HSDPA (High-Speed Downlink Packet Access) for speeding up (up to 14 Mbps) data communication in the W-CDMA system is beginning to be realized. Being an improved version of the 3G method, the HSDPA is also referred to as a 3.5G. The specification of the HSDPA is defined in detail by 3GPP (a 3rd Generation Partnership Project) which is a standardization organization for 3G wireless communication systems.
The HSDPA has the following characteristics:
(1) using one physical channel by sharing with a plurality of mobile terminals (UE) (e.g., by time-sharing according to a scheduling control);
(2) adaptively controlling a modulating method and/or an encoding method depending on a communication environment, wherein this control may be referred to as AMC (Adaptive modulation and coding) control; and
(3) using a hybrid ARQ which is a combination of a retransmission control (Auto Repeat request (ARQ) control) and error-correcting encoding processing.
Next, protocol architecture of the HSDPA will be described by using FIG. 1.
FIG. 1 shows the protocol architecture corresponding to the HSDPA (particularly layer 2). In the HSDPA, the layer 2 includes sublayers of MAC (Medium Access Control)-hs, MAC-d, and RLC (Radio Link Control).
When receiving an IP data packet added with an IP header from a higher layer, an RLC layer processing unit of a transmitting side apparatus handles the IP data packet as an RLC SDU (Service Data Unit). The RLC layer processing unit divides the RLC SDU into a plurality of data and generates a plurality of the RLC PDUs by adding an RLC header including a sequence number sequentially to each of the divided data. The RLC PDU has a fixed length during communications. As described above, if the RLC PDU is shorter than the fixed length, padding bits are added to the shorter RLC PDU to obtain an RLC PDU having the fixed length. The generated RLC PDU is given to a MAC-d processing unit of a lower layer.
A format of an RLC PDU (Protocol Data Unit) is described as follows.
FIG. 2 shows an example of a format of the RLC PDU (Protocol Data Unit). The RLC PDU shown in FIG. 2 is an RLC PDU in an Acknowledge Mode in which a transmission confirmation control of data and a retransmission control of data are possible (this RLC PDU may be referred to as an RLC AMD (Acknowledge Mode Data) PDU, and the RLC PDU used below indicates the RLC AMD PDU). This RLC PDU includes a D/C bit for distinguishing between user data and control data, sequence information (a SN (Sequence Number)) indicating the order of the RLC PDUs, a polling bit P indicating the existence or nonexistence of a transmission confirmation request, an area HE (Header Extension Type) indicating extended information of the user data, a length indicator LI, an E bit, a data storing area (DATA), and a padding bit (PAD)/a piggyback (Piggybacked STATUS PDU).
In this case, the data size of the RLC PDU is fixed to, such as 42 oct, 82 oct, or 122 oct (1 oct (octet) is 8 bits) and is not changed during communications. The RLC PDU is identified by the sequence number SN. For example, the sequence number SN is a number from 0 to the maximum number of 4095.
The RLC PDU generated in the RLC layer is given to the MAC-d processing unit. A MAC-d PDU is generated by adding a MAC-d header to the RLC PDU. A plurality of the MAC-d PDUs are made into a group to be given to a MAC-hs processing unit.
The MAC-hs processing unit generates a MAC-hs PDU which includes a plurality of the MAC-d PDUs in a data part and to which a MAC-hs header is added.
The MAC-hs PDU is given to a physical layer processing unit to be transmitted within one transmission period (TTI) and is transmitted though a HS-PDSCH (High Speed Physical Downlink Shared Channel). In advance of the transmission, an advance notice of transmission (a notice of destination and transmission form) is given to a receiving side apparatus at the destination of the transmission through a HS-SCCH (High Speed Shared Control Channel).
In the receiving side apparatus, a physical layer processing unit performs a control for giving the received MAC-hs PDU to a MAC-hs layer processing unit. The MAC-hs layer processing unit terminates the MAC-hs header and gives a plurality of the MAC-d PDUs included in the data part to a MAC-d layer processing unit. The MAC-d layer processing unit terminates each header of the plurality of the MAC-d PDUs and gives the RLC PDUs corresponding to the data part of the MAC-d PDUs to an RLC layer processing unit.
When the RLC layer processing unit receives the RLC PDUs from the MAC-d layer processing unit in the lower layer, the RLC layer processing unit replaces the RLC PDUs based on a sequence number SN included in the RLC header, generates an RLC SDU by combining a plurality of the RLC PDUs according to the sequence, and transfers the RLC SDU to the higher layer. At this time, if a sequence number SN is lacking, the RLC layer processing unit performs the control related to the transmission of a retransmit request of the RLC PDU corresponding to the lacking sequence number SN. That is, the RLC layer processing unit of the receiving side apparatus generates a signal to request the RLC layer processing unit of the transmitting side apparatus to retransmit, and the receiving side transmits this generated signal to the transmitting side apparatus through the lower layer.
By storing the transmitted RLC PDU in a buffer (a memory), the RLC layer processing unit of the transmitting side apparatus stands by waiting for the retransmit request from the receiving side apparatus until a transmission confirmation notice is received from the RLC layer processing unit of the receiving side apparatus. The RLC layer processing unit of the receiving side apparatus has a buffer (the memory) for storing the RLC PDU to generate an RLC SDU. An RLC SDU is generated when all the RLC PDUs necessary to generate the RLC SDU are completed.
The RLC layer processing unit of the transmitting side apparatus performs the transmission confirmation control by setting the polling bit P included in the RLC PDU to “1”. If the receiving side apparatus receives the RLC PDU in which the polling bit P is set to “1”, the receiving side apparatus confirms whether or not the sequence number of the RLC PDU which has been so far received is lacking. If the sequence number is not lacking, a STATUS PDU (ACK) is replied. If the sequence number is lacking, the lacking information is sent with a STATUS PDU (NACK).
The receiving side apparatus has a timer to prevent a STATUS PDU reply from occurring frequently after sending the STATUS PDU. If the receiving side apparatus notifies the transmitting side of the lacking information with the NACK, the timer is started at that time and a next STATUS PDU is not sent until the timer expires.
The transmitting side apparatus starts a timer after transmitting the transmission confirmation request. If the STATUS PDU reply is not received from the receiving side before the timer expires, it is determined that the data is lost, or the like, in wireless communication and the transmitting side apparatus again transmits a RLC PDU in which the polling bit P is set to “1”. If the transmitting side apparatus receives the STATUS PDU (ACK), it is determined that the RLC PDUs have been successfully transmitted/received so far. On the other hand, if the transmitting side apparatus receives the retransmit request with the STATUS PDU (NACK) from the receiving side apparatus, the transmitting side apparatus retransmits the RLC PDU requested.
The Japanese Laid-Open Patent Publication No. 2006-20044 discloses a memory management method. In the memory management method, in the MAC-hs sublayer, the MAC-hs PDU, which is variable length data, is divided into RLC PDU units and stored in a shared memory (a buffer) with the sequence number. Thus, it is possible to limit the increase of the memory size without using a complicated memory control method.
The above described 3.5G mobile communication system using HSDPA is expected to achieve a higher speed and a larger capacity in the fourth generation (4G) at an early stage.
Before the transition to a fourth generation, it is scheduled to proceed to one more stage called 3.9G (LTE (Long Term Evolution) ). A communication speed of the LTE is expected to be up to 100 Mbps. In the 3GPP, as a specification of the LTE at present, it is being discussed that the fixed length RLC PDU becomes variable length in the communication shown in FIG. 1 and FIG. 2. Moreover, in a case when re-transmission of the RLC PDU is performed because of the lacking RLC PDU, it is being discussed that the RLC PDU may be divided into a plurality of variable length RLC Sub PDUs to be retransmitted depending on radio line qualities or the like.
However, the retransmission by transmitting the divided RLC PDU causes confusion in the receiving side apparatus because the receiving side apparatus does not know which divided PDU (RLC Sub PDU) should be used or discarded in order to generate an RLC PDU.
Other than the case when the RLC Sub PDU is divided and retransmitted, such confusion may occur when a plurality of the retransmissions occur in a situation in which the cut portion (division of data unit) of the data unit in the M+1th retransmission can be different from the cut portion of the data unit in the Mth retransmission, in case the M+1th retransmission is performed when the retransmit request of the data related to the Mth retransmission is received.